Coined ground stud

ABSTRACT

A ground stud assembly, wherein the base is coined to form a mating cavity to receive the head of the stud and an upstanding flange around the cavity which is later squeezed over onto the head of the stud to secure it in place. The coining operation simultaneously produces a washer-like protrusion opposite the cavity to space the ground wire terminal, which is later mounted on the stud, from the base. The assembly has a single contact surface in the path of flow of the ground current.

United States Patent Willis Jan. 21, 1975 1 COINED GROUND STUD [75]Inventor: William M. Willis, Northridge,

Calif.

[73] Assignee: Lockheed Aircraft Corporation,

Burbank, Calif.

[22] Filed: June 14, 1973 [21] Appl. No.: 369,952

[52] US. Cl. 339/14 R, 339/276 11,29/511 [51] Int. Cl H0lr 3/06 [58]Field 01 Search 339/14, 276, 220; 29/511;

[56] References Cited UNITED STATES PATENTS 1,241,654 10/1917 Osgood29/511 1,432,243 10/1922 Harris 151/4173 1,761,358 6/1930 Mitchel 29/5112,675,532 4/1954 Quick 339/276 C 2,685,320 8/1954 Rosan A. 151/41732,800,247 7/1957 Appleton 29/51 1 3,451,303 6/1969 Biermannm. 151/41723,535,678 10/1970 Gulistan H 339/276 R 3,699,494 10/1972 Thompson et al.339/14 R Primary Examiner-Roy D. Frazier Assistant ExaminerRobert A.Hafer Attorney, Agent, or Firm-Bil1y G. Corber', Wi11iam Kovensky;Lowell G. Turner [57] ABSTRACT A ground stud assembly, wherein the baseis coined to form a mating cavity to receive the head of the stud and anupstanding flange around the cavity which is later squeezed over ontothe head of the stud to secure it in place. The coining operationsimultaneously produces a washer-like protrusion opposite the cavity tospace the ground wire terminal. which is later mounted on the stud, fromthe base The assembly has a single contact surface in the path of flowof the ground current.

5 Claims, 8 Drawing Figures PATENIEI] JAHZI I975 SHEEI 10F 2 PRIOR ARTPATENTED JAN 2 I I975 SHEEI EN 2 FIG. 8

convan GROUND STUD This invention relates to improved ground studs forelectrical components, and to methods of making the stud assemblies.

The invention was developed in the environment of aircraft manufacture.The prior art for grounding electrical wires in airplanes had sufferedfrom the severe disadvantages that ground studs were fairly complicatedassemblies, were quite heavy, and suffered from a corresponding highcost both in regard to the cost of the parts and the cost of assemblingthem. From the technical viewpoint, this assemblage or stack of nuts andwashers and the like provided an unacceptably large number of interfacesin the path of the electrical ground current, thus providing greaterpossibilities for electrical discontinuities, in turn increasing thechances of electrical failures in the aircraft.

In the electrical field generally, as opposed to the electrical field inaircraft, there are many different means of providing a ground between awire and a base. None of these related devices is applicable to use inaircraft for various different reasons. One such popular type is theso-called spring loaded pop" connector which is not satisfactory foraircraft use because it is difficult to disconnect, and aircraftelectronics ground studs must be readily disconnectable. Another typecomprises a spade or pin end on a wire which fits into a mating socket.Such types are unacceptable because they are susceptible to being shakenloose during flight, and aircraft ground connections must be very secureand reliable until intentionally disconnected. Another requirement whichis not met by many common types of connectors in the electrical fieldgenerally is that the terminal on the ground wire must stand off fromthe base, which stand off is required to accommodate the shape of theterminal, which is typically a transition from flat to round, and toprevent any mechanical damage to the parts.

Aircraft grounding studs must meet several mechanical and performancerequirements. The stud itself must be securely but removably fastened tothe base, the base in aircraft, of course, is the entire airframe. Thatis, the stud or bolt must be so fixed in place that it will not moveduring its own normal operation and that of the aircraft, and yet sofastened that it may be removed from the base if required formaintenance or other purposes. Further, means must be provided to causethe terminal on the ground wire to stand off of the base material, forthe reason set forth above. Another requirement is that the ground wireterminal be readily removable from its stud, and that the stud have thecapability of accommodating more than one such terminal.

As to performance requirements, the invention must provide the lowestpossible electrical resistance path from the terminal contact to theairframe structure. Where a secure interconnection of two or more metalobjects is required to establish an electrical path of constant minimumresistance, typical resistance values are 0.001 to 0.0025 ohms. Thisrequirement establishes that the minimum contacting surfaces in theelectrical path is most desirable. eliminating the need for protectivebonding of those surfaces to prevent oxidization of the surface whichwould increase the resistance.

Further, the grounding means must accomplish all of these requirementsin a simple and fool-proof manner, at low cost, with an assembly havingas low a weight as possible, and yet be capable of withstanding severevihration and shock loads.

The prior art in aviation ground studs is quite complicated having manyseparate parts. involved interlocks. and the like, with all of theconcommitant disadvantages flowing therefrom, as pointed out above. Theinvention improves upon the prior art and fulfills all of theserequirements primarily by providing a specially coined cavity in thebase. The shape of this cavity is such as to snugly receive the head ofthe ground stud or bolt, thereby preventing turning of said bolt aboutits own axis. Means are also provided in the method of the invention toform an upstanding flange of the metal flowed out from the cavity duringits coining. This flange is later squeezed inwardly over the head of thebolt to thereby hold the bolt securely in the coined cavity.Simultaneous with the coining of the cavity and the creation of theflange, the coining operation also forms a washer-like protrusion in thebase metal on the side thereof opposite the upstanding flange. Thisprotrusion also defines the bottom of the cavity. Thus, the coiningoperation forms, in the base material itself, portions therein whichserve the functions of six separate parts in a particular very popularprior art military and commercial aircraft ground stud assembly, as willbe set forth in greater detail below.

The invention was developed for use as an electrical ground stud foraircraft. However, it has other utility. a ground stud other than inaircraft, other than as a ground stud, and other uses which will presentthemselves to persons skilled in various arts. It is presently thoughtthat the invention is limited to a metallic base member since no othermaterials coin as well, and it may not be practical or feasible to coinother materials for various reasons.

The method of the invention further includes the use of more ordinarytechniques to pierce or drill or punch a hole in the washer-likeprotrusion for passage of the shank of the bolt, and certain plating orcoating operations which are performed in the usual manner for the usualreasons.

An important advantage is the single contact surface in the invention,between the wire terminal and the base washer protrusion, as opposed toa minimum of three such surfaces in the prior art, with all theattendant disadvantages of such a plurality of interfaces.

The above and other advantages of the invention will be pointed out orwill become evident in the following detailed description and claims,and in the accompanying drawing also forming a part of the disclosure inwhich: FIG. 1 is a partial cross-sectional view of a ground studassembly embodying the invention; the drawing to the left of FIG. 1marked PRIOR ART is a view of the specific prior known and used groundstud assembly replaced by the invention", FIGS. 2, 3 and 4 aresequential diagrams illustrating the coining of the cavity in the base;FIG. 5 is a perspective view partly in cross-section of the coining toolshown in FIGS. 2, 3 and 4; FIG. 6 is a perspective view of the completedcoined cavity before the stud is mounted therein; and FIGS. 7 and 8 aresequential views showing the manner in which the upstanding flange issqueezed over the head of the bolt.

Referring now in detail to the drawing, reference numeral 10 indicatesan assembled ground stud including the electrical terminal in accordancewith a preferred embodiment of the invention. Assembly 10 comprises astud I2 having a head l4 which is mounted in the base 16 by means of thecoined cavity I8, which cavity is best shown in FIG. 6. The cavity 18includes an upstanding flange 20 which is squeezed over onto the head 14of the bolt 12 to hold it in place, and a washerlike protrusion 22formed with a central opening 24 for passage of the shank 26 of thebolt. The squeezing of flange 20 and the forming of hole 24 are doneafter the coining operation. The ground wire 28 is provided with aconventional terminal 30 whose central opening is slipped over the studshank 26. The terminal 30 is held in place by a combined self-lockingnut and washer assembly 32, such devices being well known and widelycommercially available.

Use of the invention should be manifest from FIG. 1. After the stud 12is fixed into cavity I8 in the base 16, as will be described in detailbelow, the terminal 30 is tightened down onto the washer-like protrusion22 by screwing assembly 32 down along shank 26, in the usual manner. Ofcourse, a plurality of terminals 30 could be mounted on a single shank26, the exact number being controlled by the electrical requirements andstandards of any particular application. In actual use of the inventionin aircraft, the base 16 is often a bracket having a large number ofground stud assemblies on it. Another advantage of the invention is thatthe squeezed over flange is of such a thickness that a sharp blow or aforce of about pounds on the free end of the shank 26 will break theflange thereby permitting removal of ground stud 10. Alternatively, thebreak may occur around the washer-like protrusion whereby the stud andthe entire coined cavity secured thereto will be removed. Thereafter, ineither case, as a field replacement procedure, the hole remaining can beused for a conventional type of ground stud, such as the PRIOR ART"assembly shown to the left of FIG. I, or for another coined type ofground stud on a separate base fixed to the old base.

Those parts in said prior art assembly which are the same as in FIG. 1are indicated by the same reference numerals. This is not exactly trueas to bolt 12 in that the invention permits use of a slightly shorterbolt thus effecting an additional small cost and weight savings. Thisassembly includes several additional parts, each of which has a functionwhich is performed by the invention ground stud assembly 10 of FIG. I. Aretainer 34 is held to the underside of base 16 by a pair of rivets 36.This retainer 34 mates with and serves to hold the head 14 againstrotation as the remaining parts are assembled onto the shank 26 of thestud l2. Holding the stud against rotation is an important requirementbecause the base 16, be it a simple tab or part ofa large complexgrounding bracket, is often mounted on the aircraft in close quartersand in such a way that it would be difficult and often impossible to puta tool on the head 14 to hold it against rotation in assembling theremaining parts. In a large bracket carrying many studs there isfrequently no wrench clearance at all. A washer 38 is provided betweennut 14 and base 16 in order to assure that head 14 fits snugly intoretainer 34. On the opposite side of base l6, this older assemblycomprises a washer 40 and a nut 42, which parts are provided fortightening the bolt in position and protecting the base material 16 fromdamage which might be caused by such tightening. The remaining structureis the same as the invention, comprising a ground wire terminal and alock nut and washer assembly 32.

The head l4 and its mating cavity have been shown hexagonal in thedrawing for the reason that this is the commmonly used shape. Theinvention. of course. could be used with square headed bolts, whichwould dictate square cavities. or a mating ten sided shape, or in factwith any non-round shape so that the head when in its cavity could notturn about the stud axis.

The side-byside comparison of FIG. 1 and the PRIOR ART figure veryclearly shows how the invention eliminates six parts and the laborassociated therewith; namely, retainer 34, the two rivets 36, washer 38,washer 40, and nut 42. It should be pointed out, however, that it ispossible in the prior art to eliminate washer 38, depending uponrequirements in a particular aircraft and the nature of retainer 34. Theinvention also eliminates the requirement of oxidation protectionsealing between the washer and the base, and between the washer and thenut contacting surfaces.

FIGS. 2, 3 and 4 illustrate the sequential steps in the coining of thebase I6 as shown in FIG. I. It is noteworthy that the invention utilizesa coining operation to form the cavity, the washer, and the upstandingflange in the base, and does not use a stamping or pressing or othermore conventional manufacturing method. In TOOL ENGINEERS HANDBOOK,Second Edition, published by McGraw-Hill Book Co., Inc., Copyright I959,at page 55-23, under Compression Operations. it succinctly states, towit:

3. Coining operations usually force metal to flow within a die, but notout from it, so that all work surfaces are confined. The distancesthrough which the metal flows are comparatively short, but most or allof the metal flows to form new surface contours, thus necessitating highpressures. Portions of a blank or workpiece may be coined', corners ofpreviously formed or drawn cups may be built up or filled in, orindented or raised sections of a blank may be formed by coining dies..."It is this confining of the work, in combination with the high pressureof coining, which controls the flow of the metal out of the cavity andforces this material to be formed into the upstanding flange 20 and thewasher 22. Ordinary stamping and the like wherein the mate rial which ismoved out of the cavity is uncontrolled, could not be used in theinvention in that such outflow material is simply randomly pushed asideor cut out and would not form itself in the manner required by theinvention. Therefore, the term coining and the like as used in thespecification and claims herein shall be understood to limit theinvention to coining of metal in the technical sense, and any othermetal or other material forming process in which the material of thebase is flowed and controlled so as to form the cavity, the flange andthe washer. In other applications, other materials could be used as thebase, such as other ductile metals such as aluminum, copper, and thelike. Further along this line of thought, ordinary hydraulic presseswill not be satisfactory for coining, in that such machines are notintended to operate with the high pres sures which coining requires, andthe tools will deflect, or the die and/or the punch will be spongy," andother such difficulties would be experienced, all of which problemswould result in a poor flow of the base material. For this reason, it isthought that only the very rigid high quality coining presses can beused in practicing the invention.

The steps to form the coined cavity, washer and flange are illustratedby the sequential steps shown in FIGS. 2. 3 and 4. Referring to FIG. 2,the first step comprises clamping the work between a pair of pressureplates or collars 44 and 46. This first step is the confining of thework so that the material flow can be controlled. Collar 44 isassociated with a die 48, and these two parts are securely fixedtogether but the die is removable to facilitate its replacement orservicing. The die 48 is formed with a compound cavity having a majorannular die portion 50 surrounding a center deeper die portion 52.Portion 50 defines the washerlike protrusion 22. Portion 52 locates thecentral opening 24 which will be formed later and also serves anotherpurpose which will be set forth below. The collar and die 44 and 48moves together. The distance between the surface of the annular face ofcollar 44 and the annular portion 50 and the clamped work as shown inFIG. 2 defines the thickness of the washer-like pro trusion 22, andhelps to define the cavity depth. These dies may be made of conventionalmaterial such as tool steel.

On the opposite side of the work or base material 16, collar 46 slidablymounts a punch assembly 54 which is shown in more detail in FIG. 5. Thepunch assembly 54 comprises a holder 56 in which is mounted the punchproper S8. A pair of set screws 60 permit simple replacement or renewalof the punch 58. In this manner. the punch assembly can be moved by thecoining press independently of the pressure plate 46. The working headofthe punch 58 is a male impression 62 of the cavity I8, and is sized topermit the head 14 of the bolt I2 to seat in the cavity which will beformed in the base. The working face of the punch on portion 62 isformed with a relatively small protrusion 64 ofa configuration similarto the center die portion cavity 52in the die 48. An annular space 66 isformed between the inside of the punch pressure plate 46 and the maleimpression or punch 62, and it is this annular space which defines theannular flange 20. It should be noted that the outside surface of flange20 is cylindrical as defined by the pressure collar 46, and that theinside surface of the flange is of a shape matching that of the studhead 14 as defined by the punch portion 62; usually hexagonal.

Referring now to FIG. 3, the small protrusion 64 is important in thecoining operation in that it starts the base metal flowing in a moregradual manner than would a simply flat surfaced punch 62. Thus,protrusion 64 may be thought of as a pilot for the coining operation inthat it first contacts the confined base material and starts thatmaterial flowing. Additionally, this protrusion 64 serves another usefulpurpose in that it simultaneously forms a depression which serves as apilot for the piercing or drilling or punching of the hole 24 in asubsequent operation. In regard to the hole 24, a subsequent operationis required in that attempts to form this hole during coining wouldresult in the metal flowing back into that hole or up onto that punchrather than flowing in the desired directions to form the flange and thewasher.

The height of the protrusion 64 is a sensitive dimen sion in anyparticular application; consideration must be given to all of thedimensions. the materials being worked. the nature of the press beingused, and the like. If the height is too short, then excessively largeforces are required to start the coining process. If this height is toogreat, the metal flow is too harsh and a poor flange 20 is formed. Inthe successful use of the invention, working with aluminum sheets, alloy6000 series, having a thickness of 0.060 inch, using a diame ter of theprotrusion 64 of approximately 3/l6th of an inch (to serve as a pilotfor a quarter inch bolt). the protrusion height on the punch was betweenabout 0.0l5 to 0.0[8 inch.

The axial length of the male punch portion 62 defines the length of thespace 66, which in turn defines the height of the upstanding flange 20.Persons skilled in the art can control these dimensions in the die andthe punch in order to produce a cavity. washer and flange for anyparticular application. Coining presses typically have vernier strokeadjustment allowing control of dimensions in the work to plus or minus0.00l inch.

FIG. 4 illustrates the final stage in the coining operation, the punchhas moved to just short of its final posi tion, in which flnal positionthe top edge of the flange will contact the shoulder in the punch 58 atthe end of the space 66 to thereby square off the top of the flange 20,as shown in FIGS. 6 and 7.

FIG. 6 is a perspective view of the completed coined cavity prior toinsertion and securing of the stud in the cavity. The hole 24 is made bypunching or piercing or drilling or other conventional techniques. usingthe de pression formed by the protrusion 64 as a pilot if desired. Ofcourse. drill jigs of numerical control drilling machines may notrequire this pilot.

Prior to insertion of the bolt in the completed cavity, use in theaviation industry requires application of a thin film of a suitablesubstance to provide corrosion protection. This step is whollyconventional and need be no further described herein. In this regard,still an other advantage over the PRIOR ART structure shown to the leftof FIG. 1 is that the washer 40 therein must be separately coated toprotect it against corrosion. Thus. the invention eliminates not onlythe washer 40 but also the step of protecting that washer. and also thuseliminates another possible source of corrosion. and eliminates someelectrical resistance.

The length of the holder 56 above the set screw 60 with respect to theundercut in the inside wall of the pressure plate 46 is such that theend of the holder will not bottom against the shoulder formed by theunder cut. The bottom or end of the coining stroke is defined by thestroke of the coining press itself in conjunction with flow of thecoined metal to form all of the parts of the coined cavity.

After the cavity is complete and coated. the screw I2 is seated herein,and is then secured therein as shown in FIGS. 7 and 8. It should benoted that it is desirable to squeeze the upper part of the flange 20above the bolt head 14 uniformly all around the head inwardly onto thehead. The tool 68 having a cavity defined by a conical surface 70provides this squeezing action. A resilient hold down stud 72 is securedinto the tool 68 by any suitable means and serves to first contact thehead I4 to hold the screw 12 in place while the squeezing operation isperformed. In the successful use of the invention, this stud was made ofa suitable tooling plastic. A fixed base support 74 having a suitablyformed opening 76 to receive the shank 26 of bolt 12 is pro vided and isalso suitably formed to snugly receive and support the coined cavity onthe washer side thereof. The completed product of the squeezingoperation is shown in FIG. 8. It should be noted that the relativelysharp edges of the outer end of the flange are rounded as a result ofthe squeezing operation, thus avoiding any deburring problems. A uniformall-around squeezing of the flange 20 is preferred to any other sort ofsecuring technique, such as peening or staking or pining or adhesivebonding, or the like, in that such other types of securing systemsresult in discontinuities, higher labor costs, and in a very firmlyfixed assemblage. The bolt held in place by a squeezed over flange inthe manner of the invention has the advantage over a peened or staked orthe like bolt in that, in the invention method, the bolt 12 can beremoved by a sharp blow or by pressure in the event the ground studassembly should become faulty or it should be desired to replace it forany other reason. As mentioned above, the yield may be at the flange oraround the washer, and in either case a hole is left which will help inmaking a field replacement.

While the invention has been described in detail above, it is to beunderstood that this detailed descrip tion is by way of example only,and the protection granted is to be limited only within the spirit ofthe invention and the scope of the following claims.

I claim:

1. An electrical ground stud assembly comprising a metallic base member,a cavity of a predetermined shape coined into said base membercomprising an upstanding flange unitary with said base member,surrounding the opening of the cavity and extending to one side of saidbase member and a washer-like protrusion defining the bottom of thecavity and extending from and unitary with the opposite side of saidbase member, said assembly further comprising a stud having a non-roundcross-sectional shaped head and a threaded shank, the head of said studbeing located within said cavity and snugly filling said cavity inplanes perpendicular to the axis of said stud, said flange comprising aportion overlying the outside surface of said stud head, whereby saidstud is nonrotatably secured within said cavity, and an opening formedwithin said washer-like protrusion receiving and passing the shankportion of said stud.

2. The assembly of claim 1, an electrical ground terminal fitted oversaid stud shank, and means to secure said terminal against saidwasherlike protrusion.

3. The assembly of claim 2, wherein said securing means comprises acombined lock nut and washer assembly with said washer portion againstsaid terminal and said nut portion threadedly received on said studshank portion.

4. The assembly of claim 3, said base member comprising an aircraftelectrical grounding bracket, and a plurality of said ground studassemblies formed in said bracket.

5. The assembly of claim 1, wherein said stud head and said cavity areof mating hexagonal shapes.

1. An electrical ground stud assembly comprising a metallic base member, a cavity of a predetermined shape coined into said base member comprising an upstanding flange unitary with said base member, surrounding the opening of tHe cavity and extending to one side of said base member and a washer-like protrusion defining the bottom of the cavity and extending from and unitary with the opposite side of said base member, said assembly further comprising a stud having a non-round cross-sectional shaped head and a threaded shank, the head of said stud being located within said cavity and snugly filling said cavity in planes perpendicular to the axis of said stud, said flange comprising a portion overlying the outside surface of said stud head, whereby said stud is non-rotatably secured within said cavity, and an opening formed within said washer-like protrusion receiving and passing the shank portion of said stud.
 2. The assembly of claim 1, an electrical ground terminal fitted over said stud shank, and means to secure said terminal against said washer-like protrusion.
 3. The assembly of claim 2, wherein said securing means comprises a combined lock nut and washer assembly with said washer portion against said terminal and said nut portion threadedly received on said stud shank portion.
 4. The assembly of claim 3, said base member comprising an aircraft electrical grounding bracket, and a plurality of said ground stud assemblies formed in said bracket.
 5. The assembly of claim 1, wherein said stud head and said cavity are of mating hexagonal shapes. 